IsCallBack,Iscrosspagepostback,Form posting

Question

Hi all,
Please help me ...
 What is the exact difference between Iscallback and Is Crosspage Postback.
  What is the purpose of this property. What does it checks.  I came to know something  like iscallback is the result result of browser...

What is form posting in asp.net . How it differs from other state management techniques